Distillation process



Jan. 1l, 1944. c. l.. DUNN ETAL 2,339,160

' DISTILLATION PROCESS Filed Aug. 2, 1940 2 Sheets-Sheet 1 Weigh? PzrCcnf Acdonz n Lqud 909l92939495969'l9699l00 Wzqhi Per Ozm` Aceronz inLiquid Fig H lnvenors-.Clomncz l... Dunn G'xno Pzroh Patented Jan. 11,1944 nlsTILLA'rIoN PROCESS Clarence L. Dunn and Gino Pierotti, Berkeley,

Calif., assignors to Shell Development Company, San Francisco, Calif., acorporation of Delaware Application August 2,1940, Serial No. 349,758

Claims.

This invention relates to an improved distillation process for theseparation of solutions or liquid mixtures of substances the completeseparation of which is extremely difiicult by ordinary fractionationmethods. The invention relates more particularly to an improveddistillation process for the substantially complete separation of waterfrom admixture with' oxygen-containing, normally liquid, organicsubstances.

The substantially complete separation by fractionation of one or morecomponents from mixtures of liquid substances or solutions, even thoughthe component or components to be separated do not form azeotropes withother components of the mixture or solution, is often so difficult as tomake operation on a commercial scale uneconomical if not impossible.substantially complete separation of water from water-containingacetone, by distillation methods as disclosed heretofore, to obtain aproduct with a water content below, for example, about 0.5%, isdifficult and economically unattractive. A high column of large diameteris generally required and the fuel and cooling water consumption isexcessively high since the product must be distilled overhead at highreiiux.

Methods have beenl disclosed heretofore Whereinseparation of a componentfrom mixtures of liquid substances is eiectod in the presence of anadded material, termed a withdrawing agent. The purpose of thewithdrawing agent in these processes is to form an azeotrope comprisingthe withdrawing agent and the component to be separated. Althoughfacilitating to some extent the separation of components normallyseparated with great difficulty, such processes as disclosed heretofore,are exceedingly uneconomical in that the withdrawing agent must be takenoverhead as a vapor with the product to be eliminated from the mixture,thus requiring the expenditure of substantialadditional amounts of fueland cooling water. Such processes furthermore generally need elaboratecondensing and separating equipment thereby departing from thesimplicity of operation which is an essential of an economicallydesirable commercial process.

It is an object of the present invention to provide a novel andefficient process for the separation of at least one component frommixtures oi liquid substances or solutions, the substantially completeseparation of which by fractionation processes disclosed heretofore isextremely difficult, costly, and often impossible.

Another object of the invention is the provi- Thus the I sion of anovel, eiilcient distillation process lfor the separation of at leastone component from a solution or mixture of liquid substances from whichthe component or components are normally separated with diiiiculty, inwhich novel process the separation is brought about with expenditure ofsubstantially less fuel and cooling Wa.- ter than is required for asimilar separation by precesses disclosed heretofore.

Still another object of the invention is the provision of a novel,efficient and economical distillation process .for the substantiallycomplete separation of water from admixture with acetone, wherebyanhydrous acetone is obtained with far less expenditure of iuel andcooling agents than is required for the production of this product inits anhydrous state by processes as disclosed heretofore. A stillfurther object of the invention is the provision of a novel, efficientand economical distillation process for the substantially completeseparation of water from its admixture with dioxane. Other objects ofthe invention will become apparent from the following descriptionthereof.

In accordance with the invention the separation into its components ofabinary mixture of liquid substances, which separation. is impossible orcan be carried out only with difliculty by distillation processes asdisclosed heretofore, can be eiected easily and with great savings incost by fractionally distilling the mixture while maintaining throughoutthe distillation zone an added material the presence of which willincrease the content of the component to be separated as a vapor in theequilibrium vapor. The added material is selected from liquid materialshaving greater solubility for one of the components than for the other,having higher boiling points than the component for which they have thegreater solubility, and which will not form binary azeo-v tropes withthe component for which theyl have the greater solubility nor ternaryazeotropes with both components. Although the process of the inventionis applicable to the separation of components from a great number ofsolutions and mixtures of liquid substances, in order to make theinvention more readily understood it will be described herein in itsapplication to the separation of substantially all of the last traces ofwater from an oxygen-containing organic liquid such as, for example,acetone, without, how-v ever, being limited in its application to thisillustrative example.

Reference will now be made to the attached drawings forming part of thisspecification and inA which Fig. I represents composition curves showingthe per cent by weight oi acetone in the equilibrium vapors and in theliquid in contact therewith when distilling a mixture of acetone andwater in the absence of, and in the presence of toluene.

Fig. II represents composition curves showing the per cent by weight ofacetone in the equilibrium vapors and in the liquid in contact therewithwhen distilling a mixture of acetone and water in the absence of, and inthe presence of a hydrocarbon fraction boiling in the kerosene boilingrange.

Fig. III represents one form of apparatus suitable for carrying out theprocess of the invention, and

Fig. IV represents a vapor composition curve for a mixture oi acetoneand kerosene.

In the fractional distillation of aqueous acef tone, the ratio of Waterto acetone in the equilibrium vapor is less than the ratio oi water toacetone in the liquid throughout the range of composition. It has beenfound that in distilling an acetone-water mixture, the presence incontrolled amounts throughout the fractionatlng zone of a suitable addedmaterial reverses' this relationship over the range of high acetonecomposition, so that over this range of composition the ratio of waterto acetone in the equilibrium vapor is higher than the ratio of Water toacetone in the liquid. Thus the presence of over 35% of a hydrocarbonsuch as, for example, benzene, toluene, or a substantially parafilnichydrocarbon mixture having a boiling range above about 65 C., preferablyabove 100 C., such as a keroeene fraction, etc., is found to affect theliquidvapor relationships of Water and acetone so that for anacetone-water mixture containing above about 95% acetone, theequilibrium vapors will have a higher water content than the liquid inequilibrium therewith on an acetone-water basis. Such suitable addedmaterials have been termed "auxiliary reiiux throughout thespecification and claims.

The eiTect of the presence of the auxiliary reflux throughout thedistillation zone is well illustrated by Figs. I and II of the drawingsbased upon data obtained by distilling acetone-Water mixture in theabsence of, and in the presence of varying amounts of hydrocarbonauxiliary reflux at atmospheric pressure. Curve A is an enlarged plot ofthe upper portion of the liquidvapor equilibrium curve ior anacetone-water mixture showing the weight per cent of acetone in theequilibrium vapor and in the liquid in contact therewith. It is seentherefrom that the ratio of acetone to water in the vapor is greaterthan in the liquid in contact therewith. It is immediately apparent thatsubstantially complete separation of water from acetone on a commercialscale by ordinary distillation processes as known heretofore presentsserious technical and economical diillculties. Curves B, C, and D inFig. I show the enlarged upper portion of the liquid-vapor equilibriumcurves fol` acetonewater mixtures when effecting the distillation in thepresence of toluene as auxiliary reflux supplied at such a rate as tomaintain approximately 35%, 50% and 70% by weight respectively oftoluene throughout the fractionating zone. The curves show the percentby weight of acetone in the equilibrium vapor and in the liquid incontact therewith on a toluene-free basis. Similarly, curves E and F ofFig. II show the enlarged upper portion of the liquid-vapor equilibriumcurves for acetone-water mixtures when effecting the distillation in thepresence of 54% and '72% by Weight respectively of kerosene throughout 5the distillation zone. The kerosene used had a distillation range offrom 115 to 145 Cat 60 mm. It is apparent from Figs. I and II that thepresence of the hydrocarbon in increased amounts in the presence ofvarying amounts of the hydrocarbon auxiliary reux throughout thefractionating zone. The iigures are given on a hydrocarbon-free basis.

" Per cent by Weight of water on hydrocarbon-free basis In liquid 5 Invapor or No hydrocarbon present 2.9 toluene present -I 5.4 50% toluenepresent 7.3 70% toluene present 9.92 54% kerosene present 5.4 w 72%kerosene present 5.8

It is further to be noted that in the presence of the hydrocarbonauxiliary reflux the equilibrium curve based on hydrocarbon-free basis,crosses the line. In column A of the following table the water contentof the vapor and liquid on a hydrocarbon-free basis are given in percent. by weight for the points b, c, e, and J at which points curves B,C, E and F cross the 45 line respectively. Figures in column B show thewater content of the vapor in equilibrium with liquid acetone and waterfor the same ratio of acetone to water, when distilling in the absenceof the hydrocarbon auxiliary reflux. The point at which curve D crossesthe 45 line falls to the left of the section of the curve shown in Fig.I and is therefore not given here.

Point on curve A B b. (35% toluene) 6.1 3. 4 c. 50% toluene)... 8. 7 4.3 c. 54 0 kerosene) 5. 7 3.3 f. 72 D kerosene) 5.9 3.4

It would therefore seem that the effect of the presence of theauxililary reflux is the production of an apparent azeotrope betweenacetone and water although their binary mixture does not form anazeotrope under ordinary conditions. water mixture having a watercontent below that of the liquid .water-acetone mixture defined by thepoint at which the equilibrium curve crosses the 45 line, is distilledwith maintenance of an adequate amount of hydrocarbon auxiliary re- 55flux throughout the distillation zone, the water weight of wateris shownin the absence of, and

It will be seen that when an acetonea low water content, a water-richoverhead can easily beobtained thus permitting the effective andeconomical separation of the last traces of water from water-containingacetone to a degree not attainable heretofore in so economical anoperation.

' In applying this discovery to the dehydration of acetone in theprocess of the invention, the acetone-water mixture is dehydrated in a.first dehydrating step to a water content below, for example, about 5%and preferably below about 1% by weight by a distillation effected inthe absence of auxiliary refiux. The partially dehydrated acetone isthen substantially completely dehydrated by distillation in the presenceof a suitable auxiliary reflux such as, for example, kerosene ortoluene, maintained in controlled amount throughout the distillationzone. The extent to which the first dehydration step is carried out willdepend upon the nature. of the auxiliary reiiux used in the seconddehydrating zone and the concentration of the auxiliary refiuxmaintained in the second dehydrating zone. The first-dehydration stepis, however, continued to such a degree that the water content of thepartially dehydrated acetone obtained therefrom will be less than thewater content of the liquid acetone-water mixture defined by the pointat which the vapor equilibrium curve, on a hydrocarbon-free basis, forthe distillation in the second dehydrating zone crosses the 45 line.This point is, as shown above, determined by thenature of the auxiliaryreflux and its concentration throughout the second dehydrating zone.

It is to be pointed out that the process of the invention is not to beconfused with the removal ol water in its binary azeotrope with theadded material, for the binary azeotropes of all the materials namedboil at temperatures higher than the boiling point of acetone. Nor canthe effect be due to the removal of the water in its ternary azeotropewith acetone and the added material, for the stillhead temperature inall cases is well vabove the boiling point of the most volatile comeringof the partial pressures of acetone and water since this pair are knownto be easier to separate at reduced pressure and to form an azeotropecontaining 7.5% water at 150 lbs. pressure.

Although a kerosene fraction and toluene have been chosen as examples ofsuitable auxiliary reflux in the above illustrative description of theinvention, the invention is by no means limited to the use of thesematerials in the dehydration of water-containing acetone, and one ormore materials from a wide group of materials can be used comprising forexample, aromatic hydrocarbons such as benzene and xylene, hydrocarbonmixtures consisting substantially of these aromatic hydrocarbons, ethyltertiary amyl ether, saturated kctones having seven carbon atoms to themolecule, tertiary octyl alcohol, secondary amyl acetate, chlorobenzene,isodecane, substantially saturated aliphatic hydrocarbons having aboiling range above about 65 C., preferably above 100 C. Essentialrequirements of a suitable auxiliary reflux are that it have bettersolvent proppletely anhydrous acetone with a. minimum expenditure offuel and cooling water.

An oxygen-containing Vorganic liquid, such as, for example, acetone,containing water in excess of, for example. about 1 percent by weight isdrawn from an outside source through line II, controlled by valve I2,and forced by means of pump. I3 into a primary dehydrating zone. Theprimary dehydrating zone may consist of a fractionator- I4 equipped withmeans to supply heat thereto such as, for example, a reboiler, or aclosed heating coil I5 positioned in the lower part of the column. Priorto its passage into fractionator I4 the wet acetone owing through line II may be preheated by suitable means not shown in the drawings.Operation of fractionator I4 is controlled to separate a vapor fractioncomprising acetone containing less than 1% by weight of water, forexample, about 0.6% by Weight, from a liquid fraction consistingsubstantially of water. The liquid fraction is drawn from'the lower partof fractionator I4 through line I6, controlled by valve I'l, andeliminated from the system. The vapor fraction is passed from the upperpart of fractionator I4 through line I8 into a second dehydrating zone.A part of the vapors passing through line I8 is passed through line I9,controlled by valve 20 into cooler 2| whence it passes through line 22as reflux totheI upper part of column I4. The second dehydrating zonemay suitably consist of a fractionator 25.

If the charge-to the system contains less than,

for example, one per cent by weight of water it may be charged directlyto fractionator 25 by means of line 26 controlled by valve 21. Suchmaterial may be charged to the system through line 26 in addition to thematerial of higher Water content charged to fractionato I4 through lineHi. f

Within fractionator 25 the water content of the acetone is reduced toless than 0.01% by weight by the novel distillation method describedabove making use of an auxiliary reflux. In accordance therewitha,'suitable auxiliary reiiux having the above-described characteristicsis drawn from an outside source through line 29,

controlled by valve 30, and introduced into the erties ior acetone thanfor Water, that it boil at l upper part of fractionator 25 in controlledamounts at a point not above that at which condensed reiiux isintroduced into fractionator 25 as reflux. The auxiliary reflux used mayconsist, for example, of a single hydrocarbon or a mixture ofhydrocarbons. nHydrocarbons such as the lower paraffin hydrocarbons, forexample. pentane, form ternary azeotropes with acetone and water andtherefore are to be avoided. Preferred auxiliary reflux lcomprisesparaffin hydrocarbons or mixtures consisting substantially of parainichydrocarbons boiling above, for example, about C. such as a kerosenefraction having an approximate boiling range of from about C. to 14:5oC. at 60 mm. pressure. The kerosene is added to fractionator 25 incontrolled quantities to maintain a concentration throughout the columnof more than about 35%, preferably about '70%, by weight of theacetone-water mixture present in the column. If desiredthe kerosene maybe preheated to a temperature o f,

for example, from about 62 C. to about G7) C. By proper control ofthese-conditions within fractionator 25 there is obtained with acornparatively small column an overhead product rich in water and abottom product of dry acetone and kerosene. Overhead vapors fromfractionator are drawn therefrom through line 32, controlled by valve 33and will have, for example, the following approximate composition:

Percent by weight IThe acetone taken overhead from fractionator 25 willgenerally not exceed about 9.7% of the total acetone charged. Theexceedingly small kerosene content amounting to only about 0.05% of thetotal column feed, permits recycling of the vapors through line 32 andline il into fraction=1 ator i4 to recover the acetone therein. Apart ofthe vapors passing through line 32 are byu passed through lin-e 34,controlled by valve 35, and passed into condenser wherein they arecondensed. From condenser 36 liquid is passed through line 31 and line30, controlled by valve 610, into fractionator 25 as reflux. CondensateWithdrawn from condenser 30 exceeding that rem quired for reflux may bedrawn from the system through line til by `judicious manipulation oivalve til.

Liquid bottoms having, for example, the following approximatecom-position:

Percent by weight Acetone 30 Kerosene 70 is drawn from the lower part offractionator 25 through line 42 and forced therethrough by means of pump4l into fractionator 43. The water content of the acetone drawn fromfractionator 25 through line 42 will generally not exceed 0.01% byweight on a kerosene-free basis.

Within fractionator 43 separation of a. vapor fraction consisting ofanhydrous acetone from a liquid fraction consisting of kerosene iseffected. Anhydrous acetone vapors leave the upper part of fractionator43 through line 44 and pass into condenser 45 wherein they arecondensed. From condenser 45, condensed acetone is passed intoaccumulator 41. From accumulator. 41 anhydrous acetone having a watercontent below about 0.01% by weight is continuously drawn through line50, controlled by valve 5l, as the final product. A part of the actoneis drawn from line 50 and forced by means of pump 52, through line 53,into the upper part of fractionator 43 as reflux.

Fractionator 43 is provided with suitable heatlng means such as, forexample, a reboiler or a closed heating coil 54. Kerosene is drawn fromthe bottom of fractionator 43 through line 58 controlled by valve 51. Ina preferred manner of operation a part or all of the kerosene drawnthrough line 56 is forced through line 50 by means of pump 59, and intoline 29 discharging into fractionator 25. A cooler 60 is positioned inline 58 to cool kerosene recycled through line 58. If desired, thekerosene recycled through line 58 may also be subjected to indirect heatexchange with bottoms from fractionator 25 flowing through line 42, bymeans not shown in the drawings.

Selection of a suitable auxiliary reflux is guided to a substantialdegree by the ease with which it can be separated from the product. Thusthe auxiliary reflux used in the dehydration of acetone shouldpreferably have a boiling range above about 100 C. The vapor-liquidequilibrium curve, for acetone-kerosene mixtures, curve D in Fig. IV,shows the extreme ease with which these lill lili

components may be separated. It has been found that specificationacetone overhead product and bottoms with more than 99.5 per centkerosene may be obtained when utilizing as fractionator 43 a column ofonly about five theoretical plates and operating with a reflux ratio ofonly one-half.

It is to be noted that in the process of the invention minimum amountsof auxiliary reflux are vaporized within the system and substantially nocondensing of auxiliary reux is required. The process of the inventiontherefore presents a method for the production of anhydrous acetoneexceeding by far in eiliciency and economy the methods disclosedheretofore.

The process oi the invention is effected at atmospheric pressure orpressures slightly above atmospheric. The use of higher pressures is,however, not excluded from the scope of the invention and will bedetermined by the nature of the components to be separated and of theauxiliary reflux used..

Operating data for the production of anhydrous acetone in accordancewith the process of the invention are given in the following example tomore fully illustrate the invention.

Example The apparatus used is that shown in Fig. III of the drawings andparts thereof will be referred to by their respective reference numbersshown in the drawings.

Water-containing acetone is charged to the iirst dehydrating column 14,wherein the Water content of the acetone is reduced to 0.60% by weight.The acetone of reduced Water content is taken overhead from column 14and charged to the second dehydrating column 25.

Column 25.-Theoretical plates=10; reflux ratio= 10. Ratio secondaryreflux/ordinary rei1ux=2.1. Feed (overhead from column 14): 0.6% water.

Column 43.-Theoretical plates=5; reflux ratio :0.5.

Auxiliary reux.-Kerosene B. P. 115-145" C. at 60 mm. charged to column25 at such rate as to maintain approximately 70 per cent kerosenethroughout the column.

Basis.-The following gures are based on a charge of 1006 lbs. of column14 overhead to co1- umn 25:

Pounds auxiliary reflux (kerosene) circulated from column 43 to column25 per lb. of dry acetone product-2.36.

Pounds auxiliary reflux lost per 1,000 lbs. of acetone-0.4.

Aoetone recycled from column 25 to column l4-9.75% of total acetonecharged to system.

From the above data it is seen that the production of 1000 lbs. ofacetone having a water content of 0.01 per cent by weight from acetonecontaining 0.6 per cent by weight by the process in accordance with theinvention requires the vaporization of a total of 3730 lbs. ofmaterial.' Calculations from liquid-vapor equilibrium data for acetoneand water show that separation of acev tone having a water content of0.6 per cent by weight into fractions containing 0.1 and 2.4 7U byweight of water respectively with a recovery of only '75% by weight ofthe acetone fraction having a water content of 0.1% by weight wouldrequire a column of 23 ideal plates and a reflux ratio of 10. Productionof 1000 lbs. of acetone having a water content of 0.1 per cent by weightwould therefore require the vaporization of 13.750 lbs. of material.Dehydratlon of acetone from 0.5 per cent to 0.01 per cent water by theprocess of the invention requires the consumption of only 30 per cent ofthe heat consumption required to obtain a iinal product containing 0.1per cent Awater by ordinarydistillation. The extreme eiliciency andeconomy of the process of the invention are made apparent by thesefigures.

Although the invention has been described in detail in its applicabilityto the dehydration of acetone, it is to be understood that it isV notlimited in scope to this example given solely for the purpose of settingforth more clearly the nature of the invention. A great number ofoxygen-containing organic liquids may be dehydrated by the method of theinvention. Thus the process-may be applied to the separation of waterfrom its admixture with dioxane, using as auxiliary reflux the materialsmentioned above as suitable auxiliary reilux in the dehydration ofacetone. Water may be separated from admixture with isopropyl alcohol bythe process of the invention using brombenzene. as the auxiliary reux.The invention is, furthermore, not limited in its application todehydration operations and may be applied to the separation of liquidcomponents other than water from solutions or liquid mixtures.

In applying the process of the invention to the separation of at leastone component from a mixture predominating in two components A and B,the auxiliary reflux to be used will be selected from materials havingthe following characteristics:

l. Greater solubility for A than for B,

2. A boiling point, or initial boiling point, above that of A,

3. Will not form binary azeotropes with A,

4. Will not form ternary azeotropes with.A and B.

The separation of components forming azeotropic mixtures under ordinarydistillation conditions is not excluded from the scope of the invention.tion zone of a suitable auxiliary reux has been found to cause a changein the composition of the azeotrope so that it will contain a far largerproportion of one component than the natural azeotrope or will cause theazeotrope to disappear entirely. The process of the invention may beapplied for example to the substantially complete dehydration ofdioxane. Dioxane is an extremely effective agent for the azeotropicdehydration of acetic acid. Its use is restricted, however, by the.f actthat since the dioxane and water azeotrope does not stratify, a methodsuch as salting or ternary azeotropic distillation had to be resorted toheretofore to dehydrate the dioxane f or reuse. In accordance with theprocess of the invention water-containing dioxane is dehydrated bydistillation in the presence of a suitable auxiliary reiiux, such as,for example', a substantially paraflinic hydrocarbon mixture having aboiling range above the boiling point of dioxane.

The presence throughout the distilla- CII Cir

In a. preferred method of carrying out the dehydration of dioxane, thewater-containing dioxane is fractionated in the primary fractionatingzone to separate a vapor fraction consisting of the dioxane azeotropecomprising 18.8 per cent water. This azeotrope is then fractionated inthe second fractionating zone while maintaining a suitable auxiliaryreflux material such as, for example. a kerosene fraction throughout thesecond frationating zone. It has been found possible to separate a vaporfraction comprising 33.0 per cent water from a liquid fractionconsisting of substantially anhydrous dioxane and kerosene in the secondfractionating zone. Overhead from the second fractionating zone isreturned in part or entirely to the first fractionating zone.Substantially anhydrous dioxane is separated from the liquid fractionseparated in the second fractionating zone. The process of the inventionthus provides a more eiiicient method :for ,the dehydration ofwater-containing dioxane than has been available heretofore.`

The process of the invention is broadly applicable to the separation ofany solutions or liquid mixtures of substances which are separated withdifficulty or which are not at allr separable by ordinary distillationmeans and which may be separated by fractionation in the presence of athird substance having the described suitable characteristics. Theprocess of the invention is not limited in its application to theseparation of binary mixtures. For example, diisopropyl ether containingacetoney and water admixed therewith may easily be separated maintaininga kerosene auxiliary reflux throughout the distillation zone. Theauxiliary reflux having a greater solvent power for the di-isopropylether, an overhead rich in acetone and water will be obtained from thetop of the column and diisopropyl ether and auxiliary reiiux will bedrawn from the bottom of the column. 'Ihe acetonewater overhead may thenbe separated by thc method of the invention as described above.

It is to be understood that many modications of the invention may bemade without departing from the scope thereof and that it is notintended to limit the invention to any specific illustrative examples ofthe specification nor is it to be limited by the accuracy of anyoperating data or theories set forth herein for the sole purpose of moreclearly setting forth the invention. The invention is intended to belimited only by the scope of the following claims wherein it is in-'tended to claim broadly all novelty of the invention over the priorart.

We claim as o ur invention:

1. Process for dehydrating water-containing acetone comprisingfractionatlng water-containing acetone in a first fractionating zone,sepa-- rating a vapor fraction comprising acetone containing water in aquantity less than about l per cent by weight from a liquid fractionpredominating in water in the first iractionatingr zone, passing atleast a part of the vapor fraction from the first fractionating zoneinto a second fractionating zone, introducing a kerosene fraction in theliquid phase into the upper part of the second fractionating zone,maintaining said kerosene substantially in the liquid phase and at aconcentration of from about 35 per cent to per cent by weight throughoutthe second fractionating Zone, separating a water-containing vaporfraction substantially free of kerosene from a liquid fractioncomprising anhydrous acetone and kerosene in the second fractionatingtion from the second to the first fractionating zone, passing the liquidfraction fromv the second to a third fractionating zone, separatinganhydrous acetone from kerosene in the third fractionating zone.recycling at least a part of the separated kerosene from the thirdfractionating zone to the second fractionating zone, and Withdrawinganhydrous acetone as a final product from the third fractionating zone.

2. Process for dehydrating water-containing acetone comprisingfractionating water-containing acetone in a rst fractlonating zone,separating a vapor fraction comprising acetone containing Water in aquantity less than about per cent to 6 per cent by Weight from a liquidfraction predominating in water in the first frac-n tlonating zone,passing at least a part oi the vapor fraction from the firstfractionating zone into a second fractionating zone, introducing akerosene fraction in the liquid phase into the upper part of the .secondiractionating zone, maintaining said kerosene substantially in theliquid phase and at a sufficiently high concentration in the range oifrom 35 per cent to 'l5 per' cent by weight throughout the secondfractionating zone to obtain a ratio oi Water to acetone in theequilibrium vapor greater than the ratio of water to acetone in theliquid in contact therewith. separatingr a water-containing vaporfraction substantially free of kerosene from a liquid fractioncomprising anhydrous acetone and kerosene in the second fractionatingzone, passing at least a part of the vapor fraction from the second tothe iirst fractionating zone. passing the liquid fraction from thesecond to a third fractionating zone, separating a vapor fractioncomprising anhydrous acetone from a liquid fraction comprising kerosenein the third fractionating zone, recycling at least a part of the liquidfraction from the third fractionating zone to the second fractionatingzone, and withdrawing anhydrous acetone as a final product from thethird fractionating zone.

3. Process for dehydrating Water-containing acetone comprisingfractionating water-containing acetone in a rst fractionating zone,separating a vapor fraction comprising acetone containing Water in aquantity less than about 10 per cent by weight from a liquid fractionpredominating in Water in the first fractionating zone, passing at leasta part of the vapor fraction from the first to a second fractionatingzone. introducing toluene in the liquid phase into the upper part oi'the second iractionating zone, maintainingr said toluene substantiallyin the liquid phase and at a sufiiciently high concentration in therange of about per cent to '75 per cent by weicht throughout the secondfractionating zone to obtain a ratio of water to acetone in theequilibrium vapor greater than the ratio of water to acetone in theliquid fraction in contact therewith. separating` a water-containingvapor fraction substantially free of toluene from a liquid fractioncomprising anhydrous acetone and toluene in the second fractionatingzone. passim;f the liquid fraction from the second fractionating zone toa third fractionating zone. separating a vapor fraction comprisinganhydrous acetone from a liquid fraction comprising toluene in the thirdfractionating zone, recycling at least a part of the liquid fractionfrom the third fractionating zone to the second fractionating zone, andwithdrawing the vapor fraction zone, passing at least a part of thevapor fraccomprising anhydrous acetone as a final product from the thirdfractionating zone.

4. Process for dehydrating water-containing acetone comprisingfractionating water containing acetone in a rst fractionating zone,separating a vapor fraction comprising acetone containing only a minorpercentage of water from a liquid fraction predominating in water in therst iractionating zone, passing at least a part or the vaporfractionfrom the first fractionating zone to a second fractionatingzone, introducing a mixture of normally liquid substantially paraiilnlchydrocarbons in the liquid phase having a minimum boiling point aboveabout 100 il into the upper part of the second fractionating zone,maintaining said hydrocarbon substan tially in the liquid phase and at asuillclently high concentration ln the range of from about 35 per cent,to about 75 per cent by Weight throughout 2o the second fractionatingzone to obtain a ratio oi water to acetone in the equilibrium, vaporgreater than the ratio of water to acetone in the liquid in contacttherewith, separating'a water-containing vapor fraction substantiallyfree 2s oi hydrocarbons from a liquid fraction comprising anhydrousacetone and hydrocarbons in the second iractionating zone, passing theliquid fraction from the second fractionating zone to a thirdfractionating zone, separating a vapor 30 fraction comprising anhydrousacetone from a liquid fraction comprising hydrocarbons in the thirdfractionating zone, recycling at least a part of the liquid fractionfrom the third fractionating zone to the second fractionating zone, asand withdrawing the vapor fraction comprising anhydrous acetone as aiinal product fromA the third fractionating zone.

5. Process for dehydrating water-containing acetone comprisingfractionating water-contain- 40 ing acetone in a first fractionatingzone, separating' a vapor fraction comprising acetone containing only aminor percentage of water from a liquid fraction predominating in waterin the first fractionating zone, passing at least a part of the vaporfraction from the first fractionating zone to a second fractionatingzone, introducing a normally liquid substantially aromatichydrocarbonmaterial in the liquid phase having a boiling point about 100C. into the upper part of the second fractionating zone, maintainingsaid hydrocarbon substantially in the liquid phase and at a sufficientlyhigh concentration in the range of from about 35 per cent to 75 per centby Weight throughout the second fractionating zone to obtain a ratio ofwater to acetone in the equilibrium vapor greater than the ratio ofwater to acetone in the liquid in contact therewith, scparating awater-containing vapor fraction substantially free of hydrocarbons froma liquid fraction comprising anhydrous acetone and hydrocarbons in thesecond fractionating zone, Dassing at least a part of the vapor fractionfrom' the second to the iirst fractionating zone, passing the liquidfraction from the s'econd fractionating zone to a third fractionatingzone, separating a vapor fraction comprising anhydrous acetone from aliquid fraction comprising hydrocarbons in the third fractionating zone.recycling atleast a part of the vliquid fraction from the thirdfractionating zone to the second fractionating zone, and withdrawinganhydrous acetone as a nal product from the third fractionating zone.

6. In a process for recovering anhydrous acetone from an acetone-watermixture containing water in an amount less than about 5 to 6 per cent byweight, the steps of introducing the acetone-water mixture intoI airactionating zone wherein it is subjected to i'ractionating conditions,introducing a kerosene fraction in the liquid phase into the upper partof the fractionating zone, maintaining said kerosene substantially inthe liquid phase 'and at a suiliciently high concentration in the rangeof from about 35 per cent to 75 per cent by weight throughout the secondiractionating zone to obtain a ratio of water' to acetone in theequilibrium vapor greater than the' ratio of water to acetone in theliquid in contact therewith, withdrawing a. water-contain-` ing vaporfraction substantiallyiree of kerosene overhead from the fractionatingzone, withdrawing a liquid fraction comprising anhydrous acetone andkerosene from the fractionating zone, and separately recoveringanhydrous acetone from said liquid fraction.

7. In a process for recovering anhydrous acetone from an acetone-watermixture containing water in an amount less than about to-6 per cent byweight, the steps of introducing the acetonewater mixture into afractionating zone lwherein it is subjected to fractionating conditions,introducing benzene in the liquid phase into the upper.

part of the fractionating zone, maintaining said benzene substantiallyin the liquid phase 'and ata suiliciently high concentration in therange of about 35 per cent to 75 per cent throughout the fractionatingzone to obtain a ratio of water to acetone in the equilibrium vaporgreater than the ratio of water to acetone in the liquid in con,-

tact therewith, withdrawing a water-foontainin'g vapor fractionsubstantially free of benzene overhead from the fractionating zone,withdrawing a liquid fraction comprising anhydrous acetone and benzenefrom the fractionating zone.' and separately recovering anhydrousacetone from said liquid fraction.

8. In a process for recovering anhydrous acetone from an acetone-water`mixture containing only a minor percentageot water, the steps ofintroducing the acetone-'water mixture into a fractionating zone whereinit is subjected to fraci tionating conditions, introducing a normallyliquid substantially paramnic hydrocarbon material in the liquid phaseboiling' above about 65 C. into the upper part of the fractionatingzone, maintaining said hydrocarbon in the liquid phase and at asufilciently high concentration in excess of about per cent by weightthroughout the iractionating zone to obtain a ratio of water to acetonein the equilibrium vapor greater than the ratio oi.' water to acetone inthe liquid in contact therewith, withdrawing a water-containing vaporfraction substantially free ot hydrocarbons over head from thei'ractionating zone, withdrawing a liquid traction comprising anhydrousacetone and hydrocarbons from the fractionating zone. and separatelyrecovering anhydrous acetone from said liquid fraction.

9. In a process for recovering anhydrous acetone from an acetone-watermixture containing only a minor percentage of water the steps ofintroducing the acetone-water mixture into a fractionating zone whereinit is subjected to `iractionating conditions, introducing a normallyliquid hydrocarbon in the liquid phase having a boiling point above 100C. into the upper part of the fractionating zone, maintaining saidhydrocarbon substantially in the liquid phase and at a sufficiently highconcentration in excess of about 35 per cent by weight throughout thefractionating zone to obtain a ratio of water to acetone in theequilibrium vapor greater than the ratio of water to acetone in theliquid in contact therewith, withdrawing a water-containing vaporfraction substantially free of hydrocarbons over head fromthe'fractionating zone, withdrawing a liquid fraction comprisinganhydrous acetone and hydrocarbons from the fractionating zone, andseparately recovering anhydrous acetone from said liquid fraction.

l0. In a. process for recovering anhydrous acetone from an acetone-watermixture containing only a minor percentage of water, the steps ofintroducing said acetone into a fractionating column wherein it issubjected to fractionating conditions, introducing into the upper partof the fractionating column a normally liquid organic compound in theliquid phase which has a greater solvent power for acetone than forwater, which boils at atemperature above C., which is incapable offorming a binary a'zeotrope with acetone and lwhich is incapable offorming a ternary azeotrope with acetone and water at the operatingconditions, maintaining said added organic compound substantially in theliquid phase throughout the fractionating column and coordinating theconcentration of said organic compound therein with the water content ofthe acetone feed to the column so as to maintain a concentration inexcess of about 35 per cent by weight at which the ratio of water toacetone in the equilibrium vapor is greater than the ratio of water toacetone in the liquid in contact therewith, withdrawing awater-containing vapor fraction overhead substantially free of saidadded organic liquid compound, withdrawing a liquid mixture of anhydrousacetone and said added organic compound as bottom product from saidcolumn and separately recovering anhydrous acetone from said liquidmixture.

CLARENCE L. DUNN. GINO PIEROTTI.

